Conventionally, a fluorescent lamp is mainly used as a light source for use in illumination, and an illumination apparatus using an inverter lighting device to perform high frequency lighting has been widely used. However, in recent years, a light emitting diode (LED) has been attracting attention as an electrical light source other than a discharge lamp represented by a fluorescent lamp. The light emitting diode is superior to the fluorescent lamp, particularly, in terms of lifetime, and through the future technical improvements, it is expected to have a luminous efficiency exceeding that of FHF32 (high frequency fluorescent lamp of 32 W), which is a mainstream model of a fluorescent lamp for providing general lighting. However, since the light emitting diode is different from the discharge lamp and is turned on by a lighting circuit for outputting a DC power, it is impossible to use a conventional inverter lighting device as it is, and it requires a dedicated DC power source adapted for the light emitting diode characteristics and the number of light emitting diodes used.
FIG. 11 shows a power source device 100 disclosed in Japanese Patent Application Publication No. 2011-155746 (JP2011-155746A). The power source device 100 includes a buck converter including a series circuit of a first switching element Q1 and a diode D1 connected between output terminals of a DC power source E, and a series circuit of an inductor L1 and a capacitor C1 connected between both ends of the diode D1. A control circuit 101 turns on/off the first switching element Q1 by using a driving capacitor Cs as a power source. There is provided a second switching element Q2 which is turned on prior to an ON period in which the first switching element Q1 is driven on and off to cause a short circuit across the diode D1, thereby constituting a charging path to the driving capacitor Cs from a charging capacitor Cc.
In this configuration, there is provided a power source device and an illumination apparatus which can reduce the time required for a voltage across the driving capacitor Cs to be stabilized.
Further, a step-down chopper circuit is known as a typical example of a circuit for outputting a DC power. FIG. 12 shows a lighting device 200 including the step-down chopper circuit, which is disclosed in Japanese Patent Application Publication No. 2011-165587 (JP2011-165587A).
This lighting device 200 includes a control power source unit 202 which supplies a control power source Vcc to a drive control unit 201 which outputs a drive signal to turn on and off a switching element Q1 of a step-down chopper unit 203. The switching element Q1 is connected to a positive potential side of an output terminal of a DC power source unit 205, and an electrical light source (LED module) 204 which is turned on and off by the DC power is connected to a zero potential side of the output terminal of the DC power source unit 205. A capacitor C2 for the control power source, which is used to generate a drive signal of the switching element Q1, is charged by the control power source unit 202 when the switching element Q1 is turned off. An impedance element R1 having a resistance component is connected to a path for supplying a DC current to the electrical light source 204 from the positive potential side of the output terminal of the DC power source unit 205.
The drive control unit 201 has a delay means for outputting a drive signal to turn on and off the switching element Q1 at a predetermined time after the control power source Vcc is supplied.
In this configuration, it is possible to reliably generate a high voltage side control power source by a simple and inexpensive configuration even if the switching element is connected to the positive potential side of the DC power source 205.
In the power source device 100 disclosed in JP2011-155746A, in a portion of the buck converter, two expensive switching elements, i.e., the first switching element Q1 and the second switching element Q2 are required, which may cause a problem in view of manufacturing cost.
On the other hand, in the lighting device 200 disclosed in JP2011-165587A, by providing a simple and inexpensive impedance element (resistance component) R1, it is realized to determine a voltage applied to the LED module 204, i.e., a source voltage of the switching element Q1. However, it is necessary to change the design of the resistance value of the resistance component depending on a load such as the LED module 204, and a large burden/encumbrance occurs in the design and the manufacturing of the lighting device 200.